Energetic azide plasticizer

ABSTRACT

Novel multi-azido formals, acetals and ketals are disclosed, having the following generic formula ##STR1## in which R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7  and R 8  are independently selected from H, CH 3 , and CH 2  N 3 , and methods of preparation of these compounds.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to novel chemical compounds used as plasticizersin polymeric formulations. In particular, this invention relates tonovel, energetic, methylazide-substituted formals, acetals and ketals.These compounds have utility as energetic plasticizers for rocket andgun propellant and explosive formulations. A process for theirpreparation is also presented, as well as energetic compositions whichinclude the novel plasticizers.

Solid propellants, such as those used for rocket propellants, areprepared by combining a variety of materials consisting of oxidizersbinders plasticizers and a curing agent to solidify the formulation. Theplasticizers may be either energetic or non-energetic in nature.Energetic plasticizers tend to be somewhat viscous in nature, and thislimits the amount of solids that can be included in propellantformulations while maintaining good propellant processibility. Reducingthe solids loading of a propellant generally results in a loweredpropellant impulse.

This invention relates to a novel class of methylazide substitutedacetals, formals and ketals for use as plasticizers in propellantsystems, many of which are capable of being prepared from readilyavailable starting materials, and to a novel process for theirpreparation.

This invention also resides in energetic compositions which include themethylazide-substituted acetals, formals and ketals as plasticizers.Such compositions have the combined benefits of improved propellantperformance due to the energetic nature of the plasticizer, high solidsloading and ease of processibility of the propellant formulation. Theterm "energetic compositions" is intended to include rocket and gunpropellant and explosive formulations.

DETAILED DESCRIPTION OF THE INVENTION

The novel methylazide-substituted acetal, formal and ketal compounds ofthe present invention are represented by the formula: ##STR2## whereinR¹, R², R³, R⁴, R^(5l) , R⁶, R⁷ and R⁸ are independently selected fromthe group consisting of H, CH₃, and CH₂ N₃, such that the total numberof azide (N₃) groups is at least one. The term "independently selected"is used herein to indicate that two or more of the R groups may beidentical.

Examples of acetals within the above formula are those in which R¹, R²,R³, R⁴, R⁵, R⁶, R⁷ and R⁸ are as follows:

    __________________________________________________________________________    R.sup.1                                                                            R.sup.2                                                                            R.sup.3                                                                            R.sup.4                                                                            R.sup.5                                                                            R.sup.6                                                                            R.sup.7                                                                            R.sup.8                                    __________________________________________________________________________    H    H    H    CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           H    H    H    CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           H    CH.sub.3                                                                           H    CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           H    CH.sub.3                                                                           H    CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           H    CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                                                                   CH.sub.3N,                                                                         CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           H    CH.sub.2 N.sub.3                                                                   H    CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           H    CH.sub.3                                                                           H    CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                           H    CH.sub.3                                                                           H    CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3,                                                                  CH.sub.3                                                                           CH.sub.2 N.sub.3                           H    CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                                                                   CH.sub. 2 N.sub.3                                                                  CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                           H    CH.sub.2 N.sub.3                                                                   H    CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                           CH.sub.3                                                                           H    CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.3                                                                           H    CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3N,                                                                         CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub. 3                                                                  CH.sub.3                                                                           CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.3,                                                                          CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   H    CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.3                                                                           CH.sub.3                                                                           CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                                                                   CH.sub.2 N.sub.3                           __________________________________________________________________________

Within the scope of the above formula, certain embodiments arepreferred, namely those in which R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ areindependently H or CH₂ N₃ ; those in which the total number of azidegroups is at least two, preferably at least three, and most preferablyat least four; those in which R⁶ and R⁸ are each CH₂ N₃ ; those in whichR² and R⁷ are each CH₂ N₃ ; those in which R⁴, R⁵, R⁶, and R⁸ are eachCH₂ N₃ ; and those in which R¹, R², R³, R⁶, R⁷, and R⁸ are each CH₂ N₃.

The compounds of the invention may be symmetrical or asymmetric.Symmetrical compounds are preferred, i.e., those in which R¹ and R³ areidentical, R⁴ and R⁵ are identical, and R⁶ and R⁸ are identical.

The symmetrical compounds may be prepared by reacting a substitutedalcohol with an aldehyde or ketone (or suitable oligomers such astrioxane) to form either a formal. an acetal or a ketal. The aldehyde orthe ketone may or may not be substituted. The substitutions on thealcohol, aldehyde or ketone may consist of an azide group or anyfunctional group that can be replaced by an azide group. Examples of thelatter are halides such as chloride. In a typical reaction scheme, ahalogen-substituted aliphatic alcohol is first reacted with a compoundhaving an aldehyde or ketone functionality in the presence of acatalyst. This forms a formal (if formaldehyde is used). an acetal (ifacetaldehyde is used) or a ketal (if a ketone is used), which is thenreacted with a metal azide in a solvent to give the corresponding azideplasticizers. Examples of compounds having aldehyde or ketonefunctionalities are 1,3,5-trioxane. acetaldehyde, chloroacetaldehyde,acetone, and 1,3-dichloroacetone. Reactions of the alcohols with thesecompounds preferably take place at -5° C. to 35° C. in the presence of acatalyst, and are capable of producing yields above 95%. In preferredembodiments, however, the reactions are conducted at 15° C. to 25° C.with yields ranging from 75% to 85%. The reaction between the formal,acetal or ketal and the metal azide is preferably performed at 70° C. to120° C. with yields ranging from 50% to 99%. Particularly preferredreactions are those involving the use of sodium azide at 75° C. to 100°C. with dimethyl sulfoxide as the solvent, whereupon yields of 95% to99.9% may be obtained.

The asymmetrical compounds may be prepared by using a combination ofalcohols rather than a single alcohol, then isolating the desiredspecies from the product mixture using conventional purificationtechniques well known to those skilled in the art. Alternatively, theproduct mixture may itself be used without isolating single species.

The following example is intended to illustrate the invention and is inno way to be considered as a limitation on the inventive concept.

EXAMPLE 1. Preparation of bis(1,3-dichloro-2-propyl) formal

A three-neck 500-mL flask equipped with a thermometer, a mechanicalstirrer, an addition funnel, a condenser, and a positive nitrogenatmosphere were charged with 1,3-dichloro-2-propanol (51.6 g. 0.4 mole),trioxane (6.0 g. 0.2 mole as formaldehyde), and 1,2-dichloroethane (200mL). The mixture was a clear yellow solution. Concentrated sulfuric acid(29.8 g. 0.29 mole) was then added dropwise over sixteen minutes. Duringthe addition, a slight exotherm was observed, and the flask was immersedin a water bath to maintain the reaction temperature at 16°-25° C. Oncethe addition was complete, the water bath was removed and the reactionmixture was stirred at 18°-22.5° C. for 2.7 hours. The agitator was thenturned off. The lower (acid) layer (weighing 28.62 g) was removed,washed once with 50 mL 1,2-dichloroethane, and discarded. The1,2-dichloroethane layers were then combined and washed with two 300-mLportions of 1% aqueous NaHCO₃, followed by two 300-mL portions ofdeionized water. The solution was then stripped in vacuo leaving ayellow liquid, weighing 43.32 g (80.2% yield) which solidified into aslush-like consistency upon standing at ambient temperature. The productwas identified as bis(1,3-dichloro-2-propyl) formal by proton nuclearmagnetic resonance (NMR) (CDCl₃) δ 4.8 (s, --OCH₂ O--), 4.0 (m, (ClCH₂)₂CHO--), 3.6 (d, (ClCH₂)₂ CHO--).

2. Preparation of bis(1,3-diazido-2-propyl) formal (BDPF)

A three-neck 250-mL flask equipped with a mechanical stirrerthermometer, addition funnel, heating mantle and nitrogen atmosphere wascharged with dimethyl sulfoxide (75 mL) and heated to 75° C. Sodiumazide (5.05 g. 77.7 mmoles) was then added in one portion. The mixturewas heated to 95° C. The product of part 1 above (5.0 g. 18.5 mmoles)dissolved in 25 mL of dimethylsulfoxide was then added dropwise overthirty-two minutes at 94.5°-99.2° C. Upon completion of the addition,stirring was continued for four hours at 95°-99° C. The mixture was thencooled to ambient temperature, quenched with 200 mL of deionized water,and extracted with two 100-mL portions of methylene chloride. Theresulting aqueous solution was discarded, and the combined methylenechloride phases were washed with two 200-mL portions of water andstripped in vacuo to give a yellow oil, weighing 5.42 g (98.7% yield).The oil was identified as bis(1,3-diazido-2-propyl) formal by infraredanalysis (film): 2950 cm⁻¹ (CH), 2125 cm⁻¹ (N₃), 1290 cm⁻¹, 1175 cm⁻¹,1120 cm⁻¹, 1040 cm⁻¹ (OCH₂ O); and proton NMR (CDCl₃) δ 4.8 (s, OCH₂ O),3.8 m, (N₃ CH₂)₂ CHO), 3.3 (d, (N₃ CH₂)₂ CHO).

Table 1 presents physical properties and analytical results of neatBDPF, Table 2 presents calculated thermodynamic properties, and Table 3hazard properties of BDPF neat and in solvent solutions. In the hazardproperties tests, neat BDPF and BDPF solvent solutions were subjected toa series of standard tests using industry-accepted test procedures.These included Bureau of Mines Impact tests, electric spark sensitivitytests, rotary friction tests, differential thermal analyses (DTA).differential scanning calorimetry (DSC). Naval Ordnance Laboratory (NOL)detonability (card gap) tests and unconfined burning tests.

                  TABLE 1                                                         ______________________________________                                        PHYSICAL PROPERTIES and                                                       ANALYTICAL RESULTS, NEAT BDPF                                                 ______________________________________                                        Chemical structure:                                                                          (N.sub.3 CH.sub.2).sub.2 CHOCH.sub.2 OCH (CH.sub.2                            N.sub.3).sub.2                                                 Molecular Formula:                                                                           C.sub.7 H.sub.12 N.sub.12 O.sub.2                              Molecular Weight:                                                                            296.25                                                         Appearance:    Colorless liquid                                               Density:       (@ 21° C.): 1.29 gm/ml                                  Freezing Point:                                                                              -22° C.                                                 Purity (GC area %):                                                           Methylene Chloride       0.02                                                 Unknown Low Boilers      1.19                                                 Bis(1,3-dichloro-2-propyl) formal (BDCPF)                                                              0.55                                                 BDPF                     86.03                                                Polyoxymethylene Derivatives of BDPF                                                                   12.21                                                Total Chloride (wt. %):  0.24                                                 Vacuum Stability (100° C., 48 hrs.), ml/gm:                                                     2.56;                                                                         2.58;                                                                         2.85                                                 ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        THERMODYNAMIC PROPERTIES (calculated)                                         ______________________________________                                        Heat of formation, (kcal/mole)                                                                        +239.4                                                Heat of combustion. (kcal/mole)                                                                       -1307.9                                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        HAZARD PROPERTIES OF BDPF SOLVENT SOLUTIONS                                               BDPF Concentrations                                               solvent:              CH.sub.2 Cl.sub.2                                                                            DMSO                                     Test    % BDPF:   100     50    40   20    30                                 ______________________________________                                        Impact (cm at 2 kg)                                                                         42-46   >100    --   >100  >100                                 Spark sensitivity                                                                           >1.0    >1.0    --   >1.0  >1.0                                 (joules)                                                                      Rotary friction                                                                             1000-   >4000   --   >4000 >4000                                (g at 2000 rpm)                                                                             1060                                                            DTA (°C.)                                                              exotherm onset                                                                              159     169     --   198   150                                  exotherm peak 218     206     --   219   175,                                                                          188                                  DSC (°C.)                                                              exotherm onset                                                                              218     --      --   --    --                                   exotherm peak 247     --      --   --    --                                   NOL card gap using                                                                          --      pos     neg  --    --                                   zero cards                                                                    Unconfined burn of                                                                          --      --      --   --    576                                  100 mL sample (sec)                                                           ______________________________________                                    

To those skilled in the art, many modifications and variations of thepresent invention are possible in light of the above teachings. It istherefore to be understood that the present invention may be practicedotherwise than as specifically described herein and still be within thespirit and scope of the appended claims.

What is claimed is:
 1. A compound having the formula ##STR3## in whichR¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ are independently selected from thegroup consisting of H, CH₃, and CH₂ N₃ such that the total number ofazide groups is at least one.
 2. A compound in accordance with claim 1in which the total number of azide groups is at least two.
 3. A compoundin accordance with claim 1 in which the total number of azide groups isat least three.
 4. A compound in accordance with claim 1 in which thetotal number of azide groups is at least four.
 5. A compound inaccordance with claim 1 in which the total number of azide groups isthree.
 6. A compound in accordance with claim 1 in which the totalnumber of azide groups is four.
 7. A compound in accordance with claim 1in which the total number of azide groups is five.
 8. A compound inaccordance with claim 1 in which the total number of azide groups issix.
 9. A compound in accordance with claim 1 in which the total numberof azide groups is seven.
 10. A compound in accordance with claim 1 inwhich the total number of azide groups is eight.
 11. A compound inaccordance with claim 1 in which R¹ and R³ are identical, R⁴ and R⁵ areidentical, and R⁶ and B⁸ are identical.
 12. A compound in accordancewith claim 1 in which R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ areindependently selected from the group consisting of H and CH₂ N₃.
 13. Acompound in accordance with claim 1 in which R⁶ and R⁸ are each CH₂ N₃.14. A compound in accordance with claim 1 in which R² and R⁷ are eachCH₂ N₃.
 15. A compound in accordance with claim 1 in which R⁴ R⁵, R⁶ andR⁸ are each CH₂ N₃.
 16. A compound in accordance with claim 1 in whichR¹, R², R³, R⁶, R⁷, and R⁸ are each CH₂ N₃.
 17. A compound in accordancewith claim 1 in which R⁴, R⁵, R⁶, and R⁸ are each CH₂ N₃, and R¹, R², R³and R⁷ are each H.
 18. A compound in accordance with claim 1 in whichR⁴, R⁵, R⁶, and R⁸ are each CH₂ H₃ ; R¹, R², and R³ are each H; and R⁷is CH₃.